In a satellite communications system, in which multiple moving satellite communications nodes are visible to an earth-based subscriber unit, the decision as to which satellite communications node will provide services to the subscriber unit is typically based on the power received at the subscriber unit. In a typical satellite communications system, the earth-based subscriber unit measures a power received from one or more communications beam transmitted by each moving satellite communications node which is in view of the subscriber unit. If a particular communications beam possesses sufficient power to be received by the earth-based subscriber unit, the subscriber unit initiates transmissions with the particular satellite corresponding to the highest power communications beam.
However, the selection of a moving satellite communications node by an earth-based subscriber unit based purely on power received at the subscriber unit may not always be the optimum node with which the subscriber unit should communicate based on other factors. For example, a particular moving satellite communications node may already be operating at its full capacity, servicing other, similarly equipped, earth-based subscriber units. In another example, a particular moving satellite communications node may not possess sufficient primary power reserves in order to accommodate any additional earth-based subscriber units. In either example, the optimum communications node may be an adjacent node that is currently not as heavily utilized, or possess more primary power resources than the node exhibiting the highest power communications beams.
In addition to resource limitations, the selection of a particular moving satellite communications node may not be the optimum due to satellite orbit considerations. For example, a satellite possessing the highest power communications beam may be required to hand over a call to a neighboring satellite shortly after the call is initiated. This can place a strain on the satellite communications system as the neighboring satellite is forced to quickly assign channel resources in order to accept the handed over call without degrading the quality of service.
Therefore, it is highly desirable for the communication system subscriber unit to incorporate a method and system for beam acquisition based on factors other than received power from a particular moving satellite communications node. Such a method and system would allow greater sharing of call servicing resources among satellites of the communications system, and, in turn, reduce costs to users of the earth-based subscriber units. Additionally, the method and system would enable the satellite communication system to provide a greater quality of service to earth-based subscribers by reducing call hand overs between the constituent moving satellite communications nodes which comprise the system.